Method and apparatus for forming tips of screws

ABSTRACT

The invention is directed to a method of forming a tip on a fastener through the use of thread rolling dies in which the tip portion of the blank is first deformed at a point axially above the extremity to start the metal flowing or to achieve a state of plasticity followed by swaging the tip portion upwardly and inwardly to achieve the desired point configuration.

United States Patent [191 Shelton [451 Aug. 13, 1974 METHOD AND APPARATUS FOR FORMING TIPS OF SCREWS [75] Inventor: Orville Allen Shelton, Elgin, Ill.

[73] Assignee: Illinois Tool Works Inc., Chicago,

1,913,143 6/1933 Robertson 72/88 Primary ExaminerMi1ton S. Mehr Attorney, Agent, or FirmRobert W. Beart; Thomas W. Buckman Y [5 7] ABSTRACT The invention is directed to a method of forming a tip on a fastener through the use of thread rolling dies in which the tip portion of the blank is first deformed at a point axially above the extremity to start the metal flowing or to achieve a state of plasticity followed by swaging the tip portion upwardly and inwardly to achieve the desired point configuration.

6 Claims, 7 Drawing Figures PATENTEB 1 3|974 3.828.604

METHOD AND APPARATUS FOR FORMING TIPS OF SCREWS BACKGROUND OF THE INVENTION The present invention relates to a method and apparatus for deforming the tip of a fastener into a desired configuration and more particularly relates to a swaging process for forming a hemispherical point on a threaded fastener as threads are formed on the blank as by thread rolling dies.

Various applications for threaded fasteners require special point configurations, for example, set screws may require precision formed conical points or hemispherical points to achieve proper accuracy in their specific applications.

One manner of forming a particular tip configuration on a screw blank is to continuously sweep or swage the material into the desired shape. Because of the excessive drag on the material it is very difficult to swage it into the desired form in the relatively short working strokes conventionally used in thread rolling. In addition, this approach does not provide areas into which the point material can flow as it is cold worked to its desired form. The volume of the material worked may vary from one screw to the next and screws produced using this method could conceivably end up with void portions at the tip or the process could create excessive drag because there is no place for surplus material to flow.

Other prior art methods of forming a tip on a screw involve the use of cutoff dies. In this approach the tip is gradually formed or squeezed downwardly and inwardly to create a pigtail of excess material. This excess material is then knocked off or separated from the blank. However, it has been found that this method also creates excessive drag on the point of the screw as well as the undesirable effect created by the pigtail. It is only with very accurate precision tooling that the cut off portions of the die abut at the true center of the screw axis.

SUMMARY OF THE INVENTION It is an object of the invention to provide an apparatus and method for accurately forming the tip portion ofa threaded fastener during the thread rolling process.

It is a further object of the invention to provide a method and apparatus for forming a hemispherical tip extremity on a .threaded fastener.

A more general object of the invention is to form or swage the extremity of a threaded fastener during a thread rolling process in a manner which minimizes the drag forces during such an operation.

An important advantage of the invention resides in the fact that screw blanks of the same nominal size but varying actual sizes may be uniformly configured into a hemispherical point.

The above and other objects and advantages of the invention are achieved through the disclosed method and apparatus in which the tip portion is first deformed by rolling an annular depression adjacent to but above the extremity of the tip portion. This initial swaging or working of the blank material essentially places that particular region of the screw in a state of plasticity and reduces the drag forces required to further deform the tip. After the tip portion has initially been worked or BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of the tip forming tool incorporated in the invention.

FIG. 2 is a front elevation view of one of a pair of thread rolling dies used in the invention associated with the tip forming tool.

FIG. 3 is a partial end view of FIG. 2 taken from the left end thereof and absent the fastener blank for clarity purposes.

FIG. 4 is a partial top plan view of the thread rolling die and tip forming tool shown in FIG. 2 again absent the fastener blank for clarity purposes.

FIGS. 5, 6 and 7 are cross-sectional views showing the various configurations of the fastener blank corresponding to stations B, C and D in FIG. 2 as the fastener progresses between a pair of reciprocating dies.

DETAILED DESCRIPTION OF THE INVENTION Referring now more specifically to the drawings, it will be seen that the invention contemplates the use of a tip forming tool 10 in conjunction with a thread rolling die block 12 during conventional thread rolling operations. As will be understood, such operations require a pair of relatively reciprocating thread rolling die blocks such as 12 and 14. The die blocks are conventionally provided with a plurality of uniformly spaced diagonal or oblique angled lengthwise grooves and intervening ribs described broadly as 13 in FIGS. 2 and 3.

As shown in FIGS. 2-4, the tip forming tool 10 is a die member conforming generally in length and width with its associated thread rolling die block 12 and is placed beneath the die block to swage the tip portion of the fastener blank 30. While the tip forming tool 10 is shown to be an element separable from the die block 12, it should be understood that a unitary die block can be constructed incorporating the thread forming surfaces 12 as well as the tip forming and swaging surfaces on the tool 10 into one unit without fundamentally changing the invention.

Turning to FIG. 1, the detailed construction of the tip forming tool 10 can be shown to consist of three regions along the longitudinal extent of the working edge of the tool. The first longitudinal extent of the tool includes a rib 16 which extends laterally from the die block and thread forming surfaces 13 and is essentially an extension of the top face of the tool 10. From FIGS. 1, 2 and 3, it will also become apparent that the rib 16 extends generally parallel to the path of reciprocation of the dies and is situated and designed to form an annular depression in the blank 30 in a plane which is generally perpendicular to the axis of the plane. Since the rib 16 is closely adjacent to the lowermost portion of the thread rolling die block 12, it will swage the tip portion of the blank at a position above the extremity of the blank. The purpose of the particular positioning of this rib will be more fully described hereinafter relative to the operation of the apparatus and the method of forming the tip. v

A second longitudinal extent along the working edge of the tool includes a ramp-like swaging surface 18 which begins approximately where the rib l6 ends and which extends upwardly from the lower face of the block 10. This ramp 18 has a compound slope. As the ramp extends upwardly along the longitudinal extent of the die block 10 to merge with the third section 20, it also includes a degree of slope inwardlyor toward the die block. A further detailed description of the ramp and the purposes therefore will be set forth hereinafter during a detailed description of the complete method of rolling the blank.

A third and final point forming surface along the longitudinal working edge of the tool 10 is, in the preferred embodiment, a radiused forming surface, which when viewed in cross section, as in FIG. 7, is a quadrant of a circle. This radiused surface merges with the ramp 18 and serves to wipe or swage the tip into the final desired configuration. In the preferred embodiment, the final configuration is to be a hemisphere. It should be noted that the swaging section is designed to extend laterally from the thread rolling die 12 a greater distance than the lateral extension of the rib l6 and at least far enough to capture and swage the tip portion up to and including the center line of the blank so a completely formed tip results from the operation. The use of a single tool 10 rather than a pair of coacting reciprocating tools also allows the tip of the blank to be accurately and fully formed.

FIGS. 5, 6 and 7 show various stages of tip formation taken respectively at stations B, C and D as shown in FIG. 2. In conventional thread rolling practice there will be a stationary die and a movable die. In the embodiment described herein, die block 12 and the associated tip forming tool 10 are shown as the moving die while die block 14 is the stationary die block. As the blank 30 progresses along the longitudinal extent of the die block 12 and tip forming tool 10, it first is deformed by rib 16. At station B, the blank will have been deformed with an annular depression 26 and a slight concavity at the tip extremity 28. Since the extremity of the blank is not constrained, the material is free to flow accordingly. This freedom of flow is important in that the initial swaging operation performed by the rib 16 has as one of its prime purposes initiating the cold flowing or movement of the material in the tip portion.

In starting the metal at the tip portion of the blank flowing, the portion then achieves a certain state of plasticity which substantially reduces the drag force exerted on the tip extremity during subsequent stations along the working edge of the tool which swage it into a final desired configuration. The initial swaging operation performed by the rib 16 also creates two areas into which material may freely flow during the final stages of the tip formation. These areas are, of course, the depression 26 and the concavity 28.

As the blank progresses along the longitudinal extent of the tool 10, the portion beneath the annular depression 26 is progressively swaged upwardly and inwardly by the ramp 18. This operation starts near the end of the initial depression forming operation and the metal at the tip portion is still relatively plastic and somewhat easy to form. At station C, which is best represented by FIG. 6, the blank has begun to be deformed upwardly and inwardly and the material swaged during this operation tends to fill in voids such as 26 and 28.

The next and final stage of the tip formation occurs when the blank reaches the wiping surface 20. At this point at least half of the tip portion is captured and wiped to cause formation of the desired tip configuration, which in the preferred embodiment is a hemispherical point. Since the wiping portion 20 is essentially a shelf extending laterally outwardly from the die block 12 to at least the center line axis of the fastener blank, at least one-half of the tip portion is captured and swaged so there will be no excess material or pigtail formed and also an extremity will be formed which has a true center.

Of course, it should be understood that the preferred embodiment of forming a hemispherical point is only illustrative of a configuration which can readily be obtained with the invention. A screw including such a hemispherical point is frequently used as an adjustment screw or the like where a true center is important to the application. However, other point configurations which heretofore have been difficult to achieve because of the excessive drag involved in preparing them can be obtained through the method and apparatus of the invention.

Thus it is apparent that there has now been provided in accordance with the invention a method and apparatus for forming a high quality product with a fully and accurately configured tip portion. And while the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit and broad scope of the appended claims.

I claim:

I. A thread rolling and point forming die for use in relatively reciprocating die pairs for threading a blank and configuring the point on the blank, including a block having thread forming surfaces, a point forming tool associated with the thread rolling die and located below said die, the point forming tool having a first longitudinal portion including means for swaging an annular depression on a blank at a position axially above the tip extremity, a second longitudinal portion including work swaging surfaces which include means to capture the tip extremity and deform the extremity upwardly and inwardly to fill in the depression while forming the tip extremity to a predetermined configuration.

2. A thread rolling and point forming die in accordance with claim 1, wherein the means for swaging the annular depression includes a rib extending laterally from the thread forming surfaces of the block and also extending generally longitudinally along the edge of the point forming tool in a plane perpendicular to the longitudinal axis of a fastener blank.

3. A thread rolling and point forming die in accordance with claim 1 wherein the second longitudinal portion of the point forming tool includes a ramp merging into a finishing ledge, the ramp extends upwardly from the bottommost surface of the tool to capture and swage the tip portion of a fastener blank upwardly and inwardly while the shelf extends generally parallel to the path of reciprocation of the relatively moving dies.

dance with claim 1 and the stationary die includes no swaging surfaces laterally opposing the point forming tool on the movable die.

6. A thread rolling and point forming die in accordance with claim 3, wherein the swaging surface of the ledge in cross section is a quadrant of a circle. 

1. A thread rolling and point forming die for use in relatively reciprocating die pairs for threading a blank and configuring the point on the blank, including a block having thread forming surfaces, a point forming tool associated with the thread rolling die and located below said die, the point forming tool having a first longitudinal portion including means for swaging an annular depression on a blank at a position axially above the tip extremity, a second longitudinal portion including work swaging surfaces which include means to capture the tip extremity and deform the extremity upwardly and inwardly to fill in the depression while forming the tip extremity to a predetermined configuration.
 2. A thread rolling and point forming die in accordance with claim 1, wherein the means for swaging the annular depression includes a rib extending laterally from the thread forming surfaces of the block and also extending generally longitudinally along the edge of the point forming tool in a plane perpendicular to the longitudinal axis of a fastener blank.
 3. A thread rolling and point forming die in accordance with claim 1 wherein the second longitudinal portion of the point forming tool includes a ramp merging into a finishing ledge, the ramp extends upwardly from the bottommost surface of the tool to capture and swage the tip portion of a fastener blank upwardly and inwardly while the shelf extends generally parallel to the path of reciprocation of the relatively moving dies.
 4. A thread rolling and point forming die in accordance with claim 1 wherein the means for swaging extend laterally outwardly from the thread forming surfaces with the means on the second longitudinal portion extending laterally beyond the means on the first longitudinal portion.
 5. A pair of relatively reciprocating thread rolling dies wherein the movable die is constructed in accordance with claim 1 and the stationary die includes no swaging surfaces laterally opposing the point forming tool on the movable die.
 6. A thread rolling and point forming die in accordance with claim 3, wherein the swaging surface of the ledge in cross section is a quadrant of a circle. 